Sound reproducing device of the pneumatic relay type



Dec 13, 1938.

0. K. KOLB s'r A SOUND REPRODUCING DEVICE OF THE PNEUMATIC RELAY TYPEFiled July 9, 1936 5 INVENTORS 07'7'0 KURT KOLB WILL/AM J0/ l/V R/CKE7'5 ATTORNEY.

Patented Dec. 13, 1938 UNiTED STATES PATENT OFFICE Otto Kurt Kolb, Chiswick, London, and William John Rickets, Edgware, England, assignors toBritish Acoustic Films, Ltd., London, England,

a British corporation Application July 9,

1936, Serial No. 89,804

In Great Britain July 24, 1935 2 Claims.

In the art of sound reproduction it has been known that a current of airor other gas may be passed through a valve which is controlled andvibrated at acoustic frequencies by a member,

5 such as a gramophone stylus or the operative element of a telephone,such valve serving thereby to setup corresponding acoustic pulsations inthe column of gas passing through it.

By directing such a modulated gas column or stream through a suitablehorn' or like acoustic coupling means, the vibrations impressed on thegas column can be efliciently communicated to the surroundingatmosphere.

In order to control correctly and usefully the flow of gas through avalve so acting, it is essential that the valveshall be retainednormally in a partly open condition, inorder that the half oscillationswhich it makes in one direction shall act to diminish the gas flow belowits mean value, whereas half oscillations in the opposite sense shallincrease the gas flow above its mean value.

With such devices, however, a difficulty is experienced in that therelatively large volume of gas flow passing through the apparatusrequires considerable power for its maintenance. A seccm! and moreserious effect is that the passage of the large air current at silentperiods or during.

the reproduction of weak sounds, causes a considerable amount of strayhissing or background noise. According to the present invention, the airor other gas used is passed through a single valve or two valves towhich are applied two controlling motions, one a representation asfaithful as possible of the actual sound vibrations to be reproduced,the second a motion which is proportional to the amplitude of theenvelope curve of the series of sound waves applied to the apparatus, orto the averaged intensity of the sound passage being reproduced. In. thedrawing, Figs. 1 and 2 are vertical cross-sections of two embodiments ofthe invention, and Figs. 3 and 4 are diagrams of circuits which may beused with these embodiments.

Fig. 5 is a modification of Fig. 3.

In one form of the device which is indicated in Figure l of theaccompanying drawing, a pneumatic control valve such as a grid or combvalve IV, vibrating laterally over a multi-slit aperture example byattachment to a moving coil IM, which, in the example, has one windingIMI which is traversed simultaneously by a phonic cin'rent representingthe sound being reproduced as regards the actual amplitudes and waveform and valve seat IS, is actuated electrodynamically, for

byan envelope current proportioned to the existing amplitude of theenvelope or intensity curve of the sound. Two separate windings may beutilized, each individually carrying one of the currents referred to.This arrangement is schematically shown in Fig. 5, the two windingsbeing and 100 which may be windings of one moving coil. In this case,the grid or comb valve is normally positioned in the closed orpractically closed position relative'to the apertures 10 in the valveseat by a suitable controlling force applied, for example, by means ofthe suspensory ribbons or ligaments Ill, H2, H3 and H4, and on thepassage of the envelope current is opened more or less proportionally tosaid current, so that at the fullest excursion of the valve its meanposition corresponds to half closure.

The envelope current may conveniently be derived by drawing from theelectrical sound repro-\ ducing channel at an appropriate point, acertain proportion of acoustic or phonic current, by then rectifyingthis and passing it ora current controlled by it, for example by meansof a thermionic valve, through one of the operating moving coil windingsof the relay device, if necessary after passing the rectified orcontrolled current through suitable amplifying and delay clrcuiteddevices of known kind.

In an alternative formof electrically operated apparatus according tothe invention, the valve of a type similar to that hereinbefore referredto may be attached to a moving magnetic armature constituting part ofany known electro-magnetic form of telephone receiver movement. In thiscase, one or two operative-windings of the tele- 31 phone receiver carrythe dual control currents hereinbefore referred to. -An apparatus ofthis kind is indicated in Figure 2 of the appended drawing, in which agrid or comb valve 2V vibrating laterally over a multi-slit aperturevalve seat 4' is connected to the reed armature 2B. of a telephonereceiver and to twosuspensory ligaments 2H and H2. The reed armatureisinfluenced by the electro-magnetic telephone system comprising two polepieces 2Tl and 2T2 carried by a 4 horseshoe permanent magnet of knowntype. The operative windings of the telephone surrounding'the two polepieces carry the envelope current and the phonic current hereinbeforereferred to. As in the previous example, the set- 5 ting of the valve isnormally in the closed position, and becomes more or less openedaccording to the amplitude of the envelope current. When one operativewinding only is employed, either on the moving coil of anelectrodynainic reproducer or I like part, or on the exciting winding ofa telephonic electro-magnet used for actuating the valve of such anapparatus, the two control ourrents, that representing the sound asregards fresecondary of the same ITWS is connected to the quency andamplitude, and that representing the envelope curve or mean intensity ofthe sound are'both passed simultaneously through the same winding bymeans of circuits, connections or couplings of the various kinds wellknown in the art.

The effect of the above described and equivalent devices constructedaccording to the invention is as follows:-

When a phonic electric current representing a sound passage to bereproduced by the device is passed through the apparatus and itsauinliary controlling means, there is applied to one of the valvescontrolling a compressed gas flow, two sets of vibrations, onerepresenting the actual sound passage, the other representing changes inthe means intensity or maximum amplitude of the sound, in such a mannerthat when feeble sounds are being reproducedaar when silent passagesoccur, one or other ofthe valves utilized serves to close almostentirely the air passage through the valve system. Consequently, thelarge useless rush of air through the valve now generally present, isavoided, and disturbing background or hissing noise is reduced to aminimum. -When sounds of larger amplitude are being reproduced,whichever valve is controlling the mean intensity or amplitude factor ofthe sound being reproduced opens more widely the air passage through thevalve system, anda volume of gas flow is permitted of such a value thatit may be modulated by the larger sound vibrations involved.

The pneumatic supply to the valve system may be provided by the use of asource of air or gas pressure, such as a small pump, working into afirst storage chamber, the pressure in which may vary and feedingthrough a reducing valve of known sensitive type into a secondarystorage chamber containing the air or other gas of substantially steadypressure, from which the said gas passes through the amplifying valvesystem to a suitable horn or like sound emitting element.

Figs. 3 and! illustrate circuit arrangements which may be used with theabove described devices.

Referring to Fig. 3, herein an amplifier IA is connected to the controlgrids of the two valves or multi-electrode electrical discharge devicesWI and N2 in the ordinary way, so that the fluctuations in itsphoniccurrent output are applied'as potential changes to these two controlgrids. Valve IV! is connected to the transformer ITW which deals withthe actual phonic current as regards wave form. The anode of valve IV!is connected through the primary of this transformer ITWP to a positivepole of supply and the to the rectifier lR which may be of anysuitabletype but is shown' as a set of bridge connected dry contact rectifiers,the output of whichisconnected also amaaee across the coil C. Thetransformer ITA thus deals with the amplitude or envelope currentapplied to the same moving element 100. A condenser IC is connected asshown in series with the secondary of transformer 'ITW for the purposeof preventing the passage of direct current through this winding TWS.

It will be obvious that with this arrangement phonic current passesthrough the condenser lC from the transformer 'ITW and rectified currentsimultaneously passes with this phonic current through the operatingcoil 100 which, being embodied in the drive unit, either in the form ofa moving coil or telephonic winding, suitably moves to open the airvalve to a wider mean position with increasing current amplitude, whenloud passages are being reproduced in the manner set forth in thespecification.

Fig. 4 represents a variant of an arrangement for carrying out thiseffect, and in this case the amplifier 8A may, at a suitable stage, havetappings which connect directly to a rectifier system BR and an outputconnection through the grid condenser 8G0 which is connected to thecontrol grid of one valve 8V! which in this arrangement controls boththe wave form and amplitude current passed through the operating coil80C. The rectifier 8R has its output connected to a potentiometerresistance 8P which bears a sliding contact to which the control grid ofthe valve 8Vl is connected, it may be -through the grid resistance 8GR.A bias battery BBB connects the cathode of the valve 8V! toonetermination of the potentiometer resistance as shown, and the potentialdiiference due to this battery is impressed in series with that due tothe fall of potential in potentiometer 8? onto the control grid of valve8Vl. The anode of the valve 8Vl connects through the transformer primarywinding 8TWP and through the operating coil 80C to a positive'source ofsupply, whilst the secondary winding BTWS of this transformer isconnected as shown through the condenser C to the same winding. In thiscase also, two currents, one the anodecurrent flowing to valve 8Vl andthe alternating current set up in transformer BTW are s multaneouslyimpressed on the operating coil.

Having now particularly described and ascertained the nature of our saidinvention, and in what manner the same is to be performed, we declarethat what we claim is:-- v

1. A sound reproducing device of the pneumatic relay type having asingle valve of the multi-port type, a fixed seating cooperatingtherewith to control the flow, of a gas column from substantially zerovalue to a maximum, means for varying the valve opening proportionallybetween a position of closure and a half open position as the amplitudeof the reproduced sound is varied, and

means for superimposing the vibrations representing the sound wave-formon said amplitude movement.

2. Asound reproducing device of the pneumatic relay type having a valveof the'multi-port type, a seat cooperating therewith to control the flowof a gas column from substantially zero value to a maximum, means forvarying-the valve opening proportionally between a position of closureand a half open position as the amplitude of the reproduced sound isvaried, and means for superimposing the vibrations representing thesound wave form on said. amplitude movement.

o'rro KURT KOLB. 4 WILLIAM JOHN RICKETS.

